This invention relates generally to electrosurgical devices for performing electrosurgery on a patient, and particularly to safety circuits for use therein.
In general, electrosurgical devices are used to make a surgical cut in a patient by contacting the area to be cut with an active electrode with passes RF (radio frequency) current. The RF current normally passes through the patient to a dispersive electrode on which the patient lies or to which the patient is otherwise connected, and thence back to an RF generator via a return lead. By making the dispersive electrode large in comparison to the active electrode and ensuring that the patient contacts a large area of the dispersive electrode, the RF current exiting the patient will not have a high density at any one point. Hence, the patient will not be burned by the RF current which exits his body.
While electrosurgery has enjoyed widespread success, it has been recognized that a patient may be accidentally burned by RF energy in the event that the return lead to the RF generator becomes inoperative. In that event, the RF current exiting the patient may find a stray path to ground back to the RF generator. Because the RF energy may flow to the stray path from a small area of the patient's body, the current density may be high and result in a burn to the patient.
Various suggestions have been made as to overcoming the potential burn hazards in electrosurgery. One such suggestion is to monitor the current in the active lead and the return lead, and, when an imbalance is detected between active lead current and return lead current, this is used as an indication that the RF current is finding a path back to the RF generator other than through the return lead. When that condition is detected, an alarm is sounded and/or the RF generator is disabled. U.S. Pat. No. 3,683,923 describes that proposed solution. However, that proposed solution does not take into account RF leakage from the active lead, which leakage may go undetected and present a hazard to the patient.
U.S. Pat. No. 3,905,373 offers a different solution by which leakage currents to ground are provided with an intentional alternate current path back to the RF generator. In addition, a current monitor in the alternate current path detects the presence of current flowing in the alternate path for sounding an alarm or disabling the RF generator.
An additional solution is described in U.S. application Ser. No. 543,489, filed Jan. 23, 1975, wherein the alternate current path is coupled between chassis ground and the return lead with a current monitor in the alternate current path.
Although both proposals for providing an alternate current path have been found to be effective, a failure of their respective monitors leaves the patient without protection.
Thus, even though the above-described electrosurgical safety circuits have contributed greatly to patient protection, particularly that described in application Ser. No. 543,489, a more fail safe and effective safety circuit is desirable.